1. Field of the Invention
The present invention relates to a video signal recording and reproducing apparatus, wherein conversion video signals are formed, in which brilliance signals and color difference signals have been inserted by time sharing during each one horizontal period. The brilliance signals and the color difference signals are compressed in the time axis through the respective time axis compressing and time-sharing inserting operations of the brilliance signals, including the synchronizing signals and the color difference signals of the recording video signals, during the recording operation. The conversation video signals are recorded on a record medium. The brilliance signals, including the synchronizing signals and the color difference signals of the video signals reproduced from the record medium, are respectively extended in the time axis during the reproducing operation. The brilliance signals, the color difference signals which are the same in the time axis as the brilliance signals, and the color difference signals of the recording video signals are respectively reproduced and formed during each one horizontal period so as to effect the output operation.
2. Description of the Prior Art
Conventionally in a video tape recorder of a timeplex system, which is one example of this type of video signal recording and reproducing apparatus, the brilliance signal of each one horizontal period (hereinafter the horizontal period is referred to as H), including the synchronizing signal of the video signal to be recorded, is compressed in the time axis to 4/5 during the recording operation. Two types of color difference signals of R-Y, B-Y (R; red color signal, B; blue color signal, Y; brilliance signal) of the video signal to be recorded are compressed in the time axis to 1/5 alternately for each 1 H. In addition, the conversation video signals, in which the brilliance signal is compressed in the time axis to 4/5 and the color difference signal of the R-Y or B-Y is compressed in time axis to 1/5, are inserted by time sharing in each 1 H, i.e., timeplex signals are formed through the time-sharing inserting operation of the brilliance signal compressed in the time axis to 4/5 and of the color difference signal of the R-Y or B-Y compressed in the time axis to 1/5. The timeplex signals are recorded on a tape which is a recorded medium.
Also, during the reproducing operation, the brilliance signal and the color difference signal, compressed in the time axis, of the video signals obtained by the reproduction of the tape, namely, the reproduction timeplex signals which are the reproduced video signals, are respectively extended in the time axis. The output brilliance signal and output color difference signal, which are the same in the time axis as the recording brilliance signal and the recording color difference signal of the recording video signals, are respectively reproduced and formed in each 1H to perform the output operation.
In the above described time axis compression and time sharing inserting operation, time axis extending operation are digitally performed by the use of an A/D converter, memory, D/A converter, etc. In this case, an analog filter or the like is not used as in the convention video tape recorder so that no interference is provided between the brilliance signal and the color difference signal so as to improve the S/N and to resolve the degree of the color recording and reproducing.
When the digital time-axis compressing operation is performed, the brilliance signal and the color difference signal are respectively converted in an A/D generally in accordance with a given speed of a clock signal. The brilliance and the chroma data provided by the A/D conversion are respectively written in the memory and are once retained. The brilliance and chroma data are respectively read from the memory in accordance with the clock signal which has a speed higher than the given speed and are converted in the D/A to provide the brilliance signal and the color difference signal compressed in the time axis with a compression rate established by the speed difference between the stored clock signal of the memory and the reading clock signal.
In a video tape recorder of the above described timeplex system, the brilliance signal and the color difference of each 1 H of the video signals to be recorded by the clock signals of 16 MHz, 4 MHz during the recording operation are respectively converted in an A/D to respectively form the brilliance data and the chroma data. The brilliance data of each 1H are stored in a random access memory (hereinafter referred to as RAM) on the brilliance side by the clock signal of 16 MHz. The chroma data of the R-Y or the B-Y of each 1 H is stored for each 1 H in the RAM on the chroma side by the clock signal of 4 MHz.
It is to be noted that the chroma data of the R-Y, B-Y of each 1 H in the video signal to be recorded are stored, in the RAM on the chroma side, alternately for each 1 H.
In addition, the RAM on the side of the brilliance data is read by the clock signal of 20 MHz. The time-axis compressing operation is effected, at a ratio between the storing clock signal of the RAM on the brilliance data side and the reading clock signal. The time axis of the brilliance signal of the video signal to be recorded is compressed into the 4/5.
Also, the RAM on the chroma data side is read by the clock signal of 20 MHz after the storing operation. The time axis compressing operation is effected, at a ratio between the storing clock signal of the RAM on the side of the chroma data and the reading clock signal, and the time axis of the color difference signal in the video signal to be recorded is compressed into the 1/5.
It is to be noted that the reading operation of the chroma data becomes a blanking period of the brilliance signal and that the brilliance data and the chroma data are sequentially read in each 1 H.
The brilliance data and the chroma data which were read in each 1H and the achromatic level data which was secured to the level of 50 IRE are composed by the time-sharing inserting operation, in the order of the brilliance data, the achromatic level data, the chroma data are converted in the D/A by the clock signal of 20 MHz. The brilliance signal of 1 H, which has been compressed in the time axis 4/5, the achromatic level signal, and the color difference signal of R-Y or B-Y compressed in time axis to 1/5, have been inserted by time sharing in each 1 H, so the timeplex signal is formed.
It is to be noted that the formed timeplex signal is compressed in the time axis even in the synchronizing signal portion of the brilliance signal. The waveform of the vertical synchronizing signal portion becomes one wherein the achromatic level signals of 50 IRE are piled up, as shown in FIG. 7, respectively for a horizontal synchronizing pulse period, an equivalent pulse period, and a vertical synchronizing pulse period. The reference character 0 in the drawing shows a pedestal level.
On the other hand, the digital time axis extending operation is required to be processed reversely to the time axis compressing operation. In the case of the video tape recorder of a timeplex system, the brilliance signal and the color difference signal, compressed in time axis, of regenerative timeplex signals are respectively converted in the A/D by the clock signal of 20 MHz and thereafter are stored respectively in the RAM on the brilliance data side and in the RAM on the chroma data side by the clock signal of 20 MHz.
Furthermore the RAM on the side of the brilliance data is read by the clock signal of 16 MHz, the RAM on the chroma data side is read by the clock signal of 4 MHz. The data which has been read from both the RAMs are respectively converted in the D/A. The time axis of the brilliance signal and the color difference signal to be converted in A/D are respectively extended into 5/4, 5 times. The brilliance signal and the color difference signal, which is the same in the time axis as the brilliance signal and the color difference signal of the video signals to be recorded are reproduced and formed in each 1 H.
The various timings such as the storing and reading timings in the RAMs on the brilliance data side and the chroma data side during the recording time and the reproducing time are determined with the respective horizontal synchronizing signals of the recorded video signal and the reproduced video signal used as a reference. In this case, the various clock signals, such as a clock signals of both the RAMs, are formed in correctly synchronous relation with the phases of the respective horizontal synchronizing signal of the recorded video signal and the reproduced video signal. The variable control operation is required from 16 MHz or 4 MHz to 20 MHz, from 20 MHz to 16 MHz or 4 MHz at a given timing with the horizontal synchronizing signal as a reference.
There is a timeplex system as one of the recording systems of picture signals in which the brilliance signal, such as SECAM and PAL signals, is compressed in the time axis to 4/5 or the color difference signal is compressed in the time axis to 1/5 so that both signals are inserted within one horizontal period during time staring, and both signals are FM modulated and are recorded on a magnetic tape. It is to be noted that this timeplex system is described at pages 134 through 138 of the November issue, 1983 in Radio Wave Science (Japanese Broadcast Publication Association Issue).
However, in the above-described convention example, the level of the color difference signal to be obtained changes, when the signal during the reproduction is different in amplitude and DC level during the recording operation, to change the hue of the reproduction picture face.
The Radio Wave Science, Nov. 11, 1983 describes the provision of a digital synchronism detaching circuit at pages 134 through 138 for the recording and reproducing operations of the above-described timeplex system. In this case, the horizontal and vertical synchronizing signals are detected to perform the synchronizing detaching operation. The signals are detached from the digital conversion signals of the brilliance signals among the video signals to be recorded and the video signals reproduced, by the digital synchronism detaching circuit. The various clock signals, such as clock signals on the RAMs, on the brilliance data side and on the chroma data side in accordance with the horizontal synchronizing signal, is obtained by the synchronism detachment.
When the horizontal and vertical synchronizing signals are detected from the digital conversion signals of the brilliance signals, of the video signals to be recorded and the reproduced video signals, and are detached in synchronism by the use of the digital synchronism detachment circuit, the sampling space of the A/D conversion for forming the digital conversion signal is limited. In this case, one sampling space, i.e., about one clock period of detection timing shift may be cause for each 1H.
The detection timing shift varies the edge of the synchronizing signal to be detached in synchronism and changes as the edge varies the clock signal.
Furthermore, when the color difference signal is sampled with 4 MHz in this circuit construction, the step of the shift register becomes 52 .mu.s.div.1/4 MHz=208, when the scanning period is 52 .mu.s, thus requiring 208 steps. As the quantization number of the color difference signal is generally 6 bits, a shift register of a great number of elements is required in such a circuit construction thus resulting in higher circuit cost and more consumption of power.